Activating process for plating



Patented Nov. 6, 1951 2,574,305 ACTIVATING PROCESS FOR PLATING Robert M.Wagner, Anderson, Ind., assignor to General Motors Corporation, Detroit,Mich., a

corporation of Delaware No Drawing. Application September 22, 1948,Serial No. 50,673

Claims. (Cl. 204-29) This invention has to do with an activating processof treating chromium plate so that a strongly adherent coating of metalmay be electrodeposited thereon without the necessity of stripping thechromium plate from the base metal.

Prior to my invention difiiculties have been encountered in attemptingto obtain a satisfactory plating of metal on a metallic part previouslyplated with chromium. Especially has this been so when attempts havebeen made to plate bright, decorative chromium on a part previouslyplated with chromium and, so far as I am aware, no commercial productionprocesses prior to my invention have permitted this to be done. In allthose prior production methods of which I am aware, parts which havebeen rejected because of incomplete coverage in the chromium platingbath, have had the chromium stripped therefrom and then have beenreplated with chromium. My invention makes it possible to replatedirectly with chromium without stripping the previously appliedchromium.

The primary object of my invention is to provide a process of activatingparts previously plated with chromium whereby strongly adherent metalliccoatings may be electroplated thereover and particularly such process inwhich chromium may be plated directly on the activated chromium plating.

My invention consists essentially in cathodically treating metallicparts entirely or partially plated with chromium in a bath or solutionconsisting essentially of nickel sulfate within the range of 6 to 32ounces per gallon of water and hydrochloric acid within the range of 6to 32 fluid ounces of commercial concentrated hydrochloric acid (37% byvolume 1101) per gallon of water for approximately ten to thirty secondsat a cathodic current density of fifteen to one hundred and fiftyamperes per square foot. The temperature of the solution may range fromroom temperature, approximately 70 F., to 125 F. Nickel anodes are used.A preferred solution is one consisting of approximately 16 ounces ofnickel sulfate and 8 fluid ounces of commercial concentratedhydrochloric acid per gallon of water.

After the activating treatment the chromium plated parts may be platedwith copper and/or nickel and/or chromium by any of the knownelectroplating baths with good adherence and appearance. The time whichmay elapse between the activation and subsequent plating is notcritical. Chromium plated parts which have been activated have beenallowed to stand in air as high as twenty-three hours prior to platingand strongly adherent electrodeposits have been obtained. It appearsthat even longer times can elapse between activation and subsequentplating.

The original part having the chromium plating thereon may be composed ofany desired metal, metals, alloy, or alloys; for example, copper, brass,nickel, steel, etc., singly or in com= bination.

Iclaim:

1. A process of activating a metallic part having a plating of chromiumthereon so that an adherent, metallic coating may be electrodepositedthereover which consists essentially in making the chromium plated partthe cathode in a solution consisting essentially of 6 to 32 ounces ofnickel sulfate and 6 to 32 fluid ounces of commercial concentratedhydrochloric acid per gallon of water, and passing direct current from anickel anode through said solution to the chromium plated part at acathodic current density within the range of 15 to 150 amperes persquare foot for a time within the range of approximately 10 to 30seconds, said solution having a temperature within the range ofapproximately 70 F. to 125 F.

2. A process of activating a metallic part havj ing a plating ofchromium thereon so that an adherent metallic coating may beelectrodeposited thereover which consists essentially in making thechromium plated part the cathode in a solution consisting essentially ofapproximately 16 ounces of nickel sulfate and 8 fluid ounces ofcommercial concentrated hydrochloric acid per gallon of water, passingdirect current from a nickel anode through said solution at a cathodiccurrent density within the range of 15 to amperes per square foot for atime of approximately 15 seconds, said solution being at approximatelyroom temperature.

3. The process of claim 1 followed by electrodepositing a metalliccoating on the activated chromium plated part.

4. The process of claim 1 followed by electrodepositing a coating ofchromium over the activated chromium plated part.

5. The process of claim 2 followed by electrodepositing a coating ofchromium directly on the activated chromium plated part.

ROBERT M. WAGNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,746,987 Bennett Feb. 11, 19301,774,901 Piersol Sept. 2, 1930 2,118,956 Wagner May 31, 1938 2,285,548Wesley June 9, 1942 2,358,995 Pinner Sept. 26, 1944 2,437,409 TuckerMar. 9, 1948 2,491,126 McGill Dec. 13, 1949 OTHER REFERENCES Journal ofthe Electrodepositors Technical Society, vol. 9, (1933-34), pages 125,126, 131, 132.

Transactions of the Electrochemical Society, vol. 57 (1940), pages 427to 434, inclusive, 443, 447, 449; vol. 88 (1946). pages 335 to 355.

1. A PROCESS OF ACTIVATING A METALLIC PART HAVING A PLATING OF CHROMIUM THEREON SO THAT AN ADHERENT, METALLIC COATING MAY BE ELECTRODEPOSITED THEREOVER WHICH CONSISTS ESSENTIALLY IN MAKING THE CHROMIUM PLATED PART THE CATHODE IN A SOLUTION CONSISTING ESSENTIALLY OF 6 TO 32 OUNCES OF NICKEL SULFATE AND 6 TO 32 FLUID OUNCES OF COMMERCIAL CONCENTRATED HYDROCHLORIC ACID PER GALLON OF WATER, AND PASSING DIRECT CURRENT FROM A NICKEL ANODE THROUGH SAID SOLUTION TO THE CHROMIUM PLATED PART AT A CATHODIC CURRENT DENSITY WITHIN THE RANGE OF 15 TO 150 AMPERES PER SQUARE FOOT FOR A TIME WITHIN THE RANGE OF APPROXIMATELY 10 TO 30 SECONDS, SAID SOLUTION HAVING A TEMPERATURE WITHIN THE RANGE OF APPROXIMATELY 70* F. TO 125* F. 